Smart Hydrogel Plus Senolytics and Exosomes Reverses Disc Degeneration in Animal Models

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain globally, yet current treatments — from pain management to surgery — fail to address the underlying biology. The disease is driven by a self-reinforcing cycle: nucleus pulposus cells (NPCs) become senescent, secreting pro-inflammatory factors that degrade the extracellular matrix (ECM), which in turn accelerates further senescence and apoptosis. Restoring disc homeostasis requires simultaneously clearing senescent cells, reducing oxidative stress, and replenishing healthy cell activity — a challenge no single existing therapy meets.

To tackle this, researchers from Zhengzhou University and collaborating institutions engineered a bifunctional anti-swelling hydrogel encapsulating the senolytic drug combination dasatinib (D) and quercetin (Q), plus nucleus pulposus-derived exosomes (NP-Exo). The hydrogel uses a dual-network polymer architecture that resists water absorption, achieving a swelling ratio of only 1.4 after 24-hour PBS immersion — dramatically lower than conventional hydrogels. Scanning electron microscopy confirmed a uniformly distributed porous internal structure conducive to sustained drug release, and lap-shear testing on porcine skin demonstrated adhesive strength of 4.18 kPa, sufficient for firm attachment to disc tissue without drug leakage.

NP-Exo were isolated from healthy nucleus pulposus cells and characterized for size, surface markers, and cargo. These exosomes carry miRNAs, proteins, and lipids that mediate intercellular communication, suppress apoptosis, and modulate local inflammation. Compared to mesenchymal stem cell-derived exosomes, NP-Exo showed superior tissue specificity within the IVD microenvironment. When combined with D+Q, the system was designed to first clear senescent NPCs via senolytic action, then replenish the disc with bioactive signals from NP-Exo to promote surviving cell activity and ECM synthesis.

Mechanistic studies revealed that the combination preserved mitochondrial membrane potential, maintained mitochondrial function, and reduced excessive reactive oxygen species (ROS) production in NPCs — three interconnected processes that collectively delay cellular senescence. By interrupting the oxidative-inflammatory feedback loop at the mitochondrial level, the system helped restore disc homeostasis rather than merely suppressing symptoms. In vitro experiments validated that D+Q selectively eliminated senescent NPCs while NP-Exo enhanced the viability and anabolic activity of remaining healthy cells.

Efficacy was validated in both rat and goat IVDD models, providing translational relevance across species with different disc sizes and biomechanical loads. In both models, the drug-loaded hydrogel system significantly restored ECM integrity — including proteoglycan content and collagen organization — compared to untreated or single-agent controls. The anti-swelling property was highlighted as particularly important: conventional hydrogels injected into the confined disc space can expand and compress surrounding neural structures, potentially worsening herniation. The 1.4 swelling ratio of this system avoids that complication entirely. The authors position this platform as a novel, clinically translatable strategy for IVDD repair, though human trials remain a future step.